1. Field of the Invention
The present invention relates to controlling the behavior of a train and, in particular, to controlling a train""s approach to grade crossings.
2. Description of the Prior Art
Grade crossing mechanisms are activated by approach circuits placed on the railroad track. These approach circuits are placed at a particular distance from the grade crossing, such that a train moving at a certain speed will activate the gates at the grade crossing at a pre-defined amount of time before the train arrives at the crossing. Unfortunately, present systems are not known to accommodate trains that are traveling at speeds that vary from that for which the approach circuit placement was designed in electrified territory where grade crossing predictors cannot be used. Therefore, a train that is traveling at half the design speed will cause the crossing gates to be activated (and traffic blocked) for twice as long as originally designed. Correspondingly, a train traveling at higher speeds will provide proportionately less warning time than the placement design specifications.
This is shown graphically in FIG. 1. In this example, the approach circuits are placed approximately 4,107 ft. in front of the grade crossing. The time between the train arriving at the approach circuit and the train arriving at the grade crossing varies between the desired 35 seconds for a train traveling at 80 MPH, and as much as 560 seconds for a train traveling at 5 MPH. The algorithm for this situation is represented in the flow chart shown in FIG. 2.
As demonstrated in this example, current grade crossing activation systems are relatively inflexible which causes significant variability in the amount of warning they provide to the public. This has safety implications in that inconsistent and/or relatively long warning times may foster undesirable behavior in certain members of the public. These certain members of the public may make assumptions about the length of time it may take the train to reach the crossing and may attempt to drive around the crossing gates, or engage in other unsafe behavior. This is a particular problem when, as noted before, the train may be moving at a very slow speed of 5 MPH.
It is an advantage of the present invention to control train operations in order to achieve a more efficient operation of an approached grade crossing. Currently, there is wide variability in the operations of grade crossing gates due to speed fluctuations and other operating characteristics of the approaching train, vehicles at the crossing gate and characteristics of the highway and rail interface. The present invention as described herein leads to significantly more xe2x80x9cefficientxe2x80x9d operation of the grade crossing where xe2x80x9cefficiencyxe2x80x9d is defined as how close the operations come to a uniform and standard time from warning to train traversal of the crossing (also known as UTW for Uniform Time Warning). The present invention utilizes Communication Based Train Control (CBTC), a device which can be appreciated by reference to the following publication: Communications among components of the rail system, including the train and intelligent grade crossing controllers, as well as some level of train control have been combined in an innovative way by the present inventors to achieve efficient operations at the crossing gate.
With the advent of CBTC systems it is possible to be more intelligent in the control of grade crossing systems. This improvement results in a more flexible system that accommodates the variations in train speed while maintaining a consistent warning time to the public. With the application of the present invention to CBTC systems it is possible to approach consistent warning times regardless of train operations, e.g., even if the train speed should tend to increase radically.
Present CBTC systems are not sufficient in and of themselves because they are not known to control train operations. The present invention shows how control of train operations in combination with a CBTC system provides a significant advantage in efficiently controlling grade crossing gates. The present invention is distinguished over the prior art at least because of its ability to significantly improve the efficiency of grade crossing operations.
According to the present invention, the amount of time between when the crossing gates are activated and when the train is actually at the crossing is more consistent. As the public becomes aware of this consistency, the public may be more likely to wait for a train to pass and avoid unsafe behavior, such as attempting to drive around the crossing gates.
As used in this description, an example of an ideal uniform time warning (UTW) is 35 seconds, but in general UTW is a variable that can be set to any value.
A graph showing the ideal warning distance for all train speeds between 0 and 80 miles per hour is shown in FIG. 3. The figure shows that regardless of the speed of the train, it would provide 35 seconds of warning time at the grade crossing. However, this is not achieved in practice. With current CBTC systems, the train can communicate location and speed information to the wayside equipment. This establishes the basis for the necessary calculations, but other factors may also need to be considered.
Current train control systems are not known to constrain the speed or acceleration of a train approaching a grade crossing. For example, a locomotive engineer may begin a rapid acceleration after activating the approach circuit for a particular grade crossing. As another example, if the train comes in to the area depicted in FIG. 3 at 5 MPH, it may accelerate from 5 MPH to 80 MPH at any point. In the worst possible condition, it could start accelerating when it is 260 ft. away from the crossing, just as an approach circuit activates the crossing gate. This would drastically reduce the warning time to well below the desired 35 seconds. In fact, the warning would be only about 9 seconds. FIG. 4 shows this example.
To eliminate the possibility of such a problem, the system could be designed such that the grade crossing gates are activated well before the efficient frontier. In FIG. 5 the thicker line represents the time when the grade crossing gates would need to be activated to assure a minimum of 35 seconds of warning time. However, this in turn translates to only a small improvement over the current art. Specifically, a train that enters from the right, travelling at 5 MPH would cause the crossing gates to go down about 6 minutes before the train arrives at the crossingxe2x80x94clearly this is not efficient operations.
The present invention is also advantageous in that it provides for a more consistent operation of the grade crossings that would be visible to the public, resulting in a public good, as more consistent and efficient grade crossing gate operations enhance the safety of the traveling public at such crossings.
The present invention is directed toward a system for controlling the movement of a train as it approaches a grade crossing to achieve a uniform time period from activation of the crossing gates to the traversal of the crossing by the train. The present invention continuously monitors the train""s movement as it approaches the crossing and at a particular point determines the train""s velocity and a time to activate the gates that satisfies the UTW. At this point the system determines an upper velocity limit that, if exceeded, will reduce the time to activate the gates below the UTW. The system continues to monitor the train""s velocity during the train""s approach. If the train""s velocity remains constant, train operations are unaffected. If the train attempts to accelerate, the train""s velocity is restricted to conform to the UTW. But, if a change of velocity is detected during the approach toward the crossing gates, the gates are immediately activated and a top velocity is enforced on the train. This combination of means ensures that the gates are down for the minimum time of 35 seconds and that the gates are consistently activated
The foregoing and still further objects and advantages of the present invention will be more apparent from the following detailed explanation of the preferred embodiments of the invention in connection with the accompanying drawing.